Systems and methods for using a power converter for transmission of data over the power feed

ABSTRACT

Apparatuses and methods include a photovoltaic energy production unit to generate electricity. A local management unit is coupled between the photovoltaic energy production unit and a connection of energy production units forming a string bus. The local management unit includes a controller and switching circuitry. The controller provide a control for the switching circuitry to deliver electrical energy to the string bus. A communication transmission modulator is associated with the local management unit. The communication transmission modulator modulates the control with data to be transmitted from the local management unit over the string bus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patent application Ser. No. 12/411,317, filed Mar. 25, 2009, which claims the benefit of Provisional U.S. Application Ser. No. 61/200,601, filed Dec. 2, 2008 and Provisional U.S. Application Ser. No. 61/200,279, filed Nov. 26, 2008. The present application also claims the benefit of Provisional U.S. Application Ser. No. 61/207,296, filed Feb. 10, 2009. The disclosures of the above-mentioned applications are hereby incorporated herein by reference.

FIELD OF THE TECHNOLOGY

At least some embodiments of the disclosure relate to photovoltaic systems in general, and more particularly but not limited to, improving the energy production performance of photovoltaic systems.

BACKGROUND

Conventional systems for transmission of data over low impedance power feed lines exist. However, these systems and methods require additional hardware for the transmission and reception of data in a solar panel system.

Many of the issues involved in sending communication signals over DC power lines also exist when sending such signals over the AC power grid. The properties of the transmission medium vary greatly, and the amount and nature of noise sources are very difficult to predict.

However, there are some important differences too. On the AC power grid, the loads are mostly of an inductive nature, and some loads may be resistive and a few subtly capacitive. In contrast, on a DC power bus, virtually all loads and sources are capacitive in nature. Another key difference lies in the use of transformers to convert between different voltage levels on an AC grid that cannot be similarly employed on a DC bus. Hence, a majority of sources and loads on a DC bus employ electronic DC-DC converters, which are very strong noise emitters.

There are many challenges to communicating digital data quickly and reliably over a set of wires intended to conduct electrical energy. For a variety of reasons, the signal carrier frequency should not exceed 500 kHz, so as to avoid the antenna effects, and avoid excessive signal attenuation and unintentional electromagnetic radiation. Power line carrier frequency is typically between 90 kHz and 490 kHz for small power line network line for, for example, a residence. A larger commercial power line installation must further limit the maximum carrier frequency so that the effective length of the wires does not exceed ⅛ of the carrier wave length.

Low carrier frequency in turn means that the rate of signal than can be modulated on such a carrier is also very low, so that a certain payload to carrier ratio is maintained. The signal rate that can be carrier by a frequency is also limited by severe noise and attenuation typical to power lines. This is because the slower the signal rate, the more energy is carrier by a single symbol (bit), and with more energy in a bit, the less likely it is to be corrupted in transmission.

There are several types of products on the market at this time to address the needs of power line communications. Broadband communication products deliver local area network performance but can not handle more than just a handful of nodes on the network. Such products lack the robustness and reliability that is needed for a sensor network.

The narrowband power line communication products can be further divided into two types: the solutions involving a single or dual carrier tones and the newer solutions mostly involving a kind of spread spectrum technique involving a large number of carrier tones or a digitally synthesized equivalent.

Solar system installers take a large guard band (or safety margin) to make sure the voltages don't cross the 600V or 1000V limits in the United States and the European Union, respectively. That limitation inhibits them from installing more solar panel modules, often referred to as “modules” or “panels,” in series to reduce the cost of combiner boxes or string inverters. When solar modules are connected in series or in mesh configurations, there can be a problem in which weaker modules not only produce less energy but also affect other modules' capabilities to deliver energy in the same string or wiring section.

In the solar panel industry, the pressure to reduce costs is increasing. While certain features may be desired, there is more pressure to dramatically reduce cost, which means delivering added functionality at little or virtually no cost.

SUMMARY OF THE DESCRIPTION

Systems and methods in accordance with the present invention are described herein. Some embodiments are summarized in this section.

In one of many embodiments of the present invention, apparatuses and methods include a photovoltaic energy production unit to generate electricity. A local management unit is coupled between the photovoltaic energy production unit and a connection of energy production units forming a string bus. The local management unit includes a controller and switching circuitry. The controller provide a control for the switching circuitry to deliver electrical energy to the string bus. A communication transmission modulator is associated with the local management unit. The communication transmission modulator modulates the control with data to be transmitted from the local management unit over the string bus.

Other embodiments and features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. FIGS. 1-3A illustrate local management units according to some embodiments.

FIG. 4 illustrates a photovoltaic system according to one embodiment.

FIG. 5 illustrates a solar panel according to one embodiment.

FIGS. 6-8 show methods to improve performance of a photovoltaic system according to some embodiments.

FIG. 9 illustrates a local management unit according to one embodiment.

FIG. 10A is a plot of carrier frequency for a local management unit according to one embodiment.

FIG. 10B illustrates a subsystem including a local management unit according to one embodiment.

FIG. 11A illustrates a photovoltaic system according to one embodiment.

FIG. 11B illustrates a receiver of a photovoltaic system according to one embodiment.

FIG. 12 illustrates a local management unit according to one embodiment.

FIGS. 13-18 illustrate operation of the local management unit illustrated in FIG. 12.

FIG. 19 illustrates a local management unit and transmission modulator according to one embodiment.

DETAILED DESCRIPTION

The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding. However, in certain instances, well known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure are not necessarily references to the same embodiment; and, such references mean at least one.

When solar modules are connected in series or mesh configuration, there can be a problem in which weaker modules not only produce less energy but also affect other modules in the same string or wiring section. By measuring one can determine that a few modules are weaker than the others in most commercially installed strings. Thus, the string is generating less power than the sum available at each module if modules were operated separately.

At least one embodiment of the present disclosure provides methods and systems to switch on and off weak modules in the string in a way that the current on the string bus from the good modules won't be affected by the weak modules.

The present invention allows transmission of data from solar modules to a central (or system controller management) unit and other local management units in an energy production or photovoltaic system without adding significant cost. One embodiment of the present invention involves using the typically undesired electrical noise produced when operating local management units (sometimes referred to as “controllers” or “converters”) to act as a carrier system for data to be transferred. As there are a multitude of solar modules, each can be run on a slightly different frequency. Such an approach allows a receiver in the energy production or photovoltaic system to identify the carrier signal of each local management unit separately. This approach has the added benefit of reducing the overall system noise, because each local management unit sends “noise energy” in a different part of the spectrum, thus helping to avoid peaks.

FIGS. 1-3 illustrate local management units according to some embodiments. In FIGS. 1-3, local management units (101) are used to switch on and off the solar module (102) periodically to improve the energy production performance of the photovoltaic systems connected, at least in part, in series. A local management unit may be variously referred to as a solar module controller (or converter) or link module unit. One example of a local management unit is any of the various local management units (solar module controllers) offered by Tigo Energy, Inc. of Los Gatos, Calif.

In FIG. 1, a management unit (101) is local to the solar module (102) and can be used to periodically couple the solar module (102) to the serial power bus (103) via the switch Q1 (106), to improve the total power output for the string of solar modules connected to the serial power bus in series.

The local management unit (LMU) (101) may include a solar module controller to control the operation of the solar module (102) and/or a link module unit to provide connectivity to the serial power bus (103) for energy delivery and/or for data communications.

In one embodiment, the command to control the operation of the switch Q1 (106) is sent to the local management unit (101) over the photovoltaic (PV) string bus (power line) (103). Alternatively, separate network connections can be used to transmit the data and/or commands to/from the local management unit (101).

In FIGS. 1 and 2, the inputs (104 a, 104 b, 104 c) to the local management unit (101) are illustrated separately. However, the inputs (104 a, 104 b, 104 c) are not necessarily communicated to local management unit (101) via separate connections. In one embodiment, the inputs are received in the local management unit via the serial power bus (103).

In FIG. 1, the solar module (102) is connected in parallel to the capacitor C1 (105) of the local management unit (101). The diode D1 (107) of the local management unit (101) is connected in series in the serial power bus (103) which may or may not be part of an overall mesh configuration of solar modules. The switch Q1 (106) of the local management unit can selectively connect or disconnect the solar module (102) and the capacitor C1 (105) from a parallel connection with the diode D1 (107) and thus connect or disconnect the solar module (102) from the serial power bus (103).

In FIG. 1, a controller (109) of the local management unit (101) controls the operation of the switch (106) according to the parameters, such as duty cycle (104 a), phase (104 b) and synchronization pulse (104 c).

In one embodiment, the controller (109) receives the parameters (104 a, 104 b, 104 c) from a remote management unit via the serial power bus (103) or a separate data communication connection (e.g., a separate data bus or a wireless connection). In some embodiment, the controller (109) may communicate with other local management units connected on the serial power bus (103) to obtain operating parameters of the solar modules attached to the serial power bus (103) and thus compute the parameters (e.g., 104 a and 104 b) based on the received operating parameters. In some embodiment, the controller (109) may determine the parameter (e.g., 104 a and 104 b) based on the operating parameters of the solar module (102) and/or measurements obtained by the controller (109), without communicating with other local management units of other solar modules, or a remote system management unit.

In FIG. 2, a system (100) has a local management unit (101) coupled to the solar module (102). The local management unit (101) is connected between the solar module (102) and the string bus (103) to improve the total power output for the whole string on the serial power bus (103). Commands to the local management unit (101) can be sent over the photovoltaic (PV) string bus (power line) (103). To make the figure more clear, the inputs (104 a, 104 b, 104 c) to the controller (109) of the local management unit (101) were drawn separately, which does not necessarily indicate that the inputs (104 a, 104 b, 104 c) are provided via separate connections and/or from outside the local management unit (101). For example, in some embodiments, the controller (109) may compute the parameters (104 a, 104 b, 104 c) based on measurements obtained at the local management unit (101), with or without data communications over the serial power bus (103) (or a separate data communication connection with other management units).

In FIG. 2, the local management unit (101) is connected in one side to the solar module (102) in parallel and on the other side in series to a string of other modules, which may or may not be part of an overall mesh configuration. The local management unit (101) may receive, among others, three inputs or types of input data, including a) requested duty cycle (104 a), which can be expressed as a percentage (e.g., from 0 to 100%) of time the solar module (102) is to be connected to the serial power bus (103) via the switch Q1 (106), b) a phase shift (104 b) in degrees (e.g., from 0 degree to 180 degree) and c) a timing or synchronization pulse (104 c). These inputs (e.g., 104 a, 104 b and 104 c) can be supplied as discrete signals, or can be supplied as data on a network, or composite signals sent through the power lines or wirelessly, and in yet other cases, as a combination of any of these input types.

In FIG. 2, the local management unit (101) periodically connects and disconnects the solar module (102) to and from the string that forms the serial power bus (103). The duty cycle (104 a) and the phase (104 b) of the operation of the switch Q1 (106) can be computed in a number of ways to improve the performance of the system, which will be discussed further below.

In FIG. 2, the local management unit (101) includes a capacitor C1 (105) and a switch Q1 (106), as well as a diode D1 (107). In FIG. 2, the diode D1 (107) is supplemented with an additional switch Q2 (108), which acts as a synchronous rectifier to increase efficiency. In one embodiment, the additional switch Q2 (108) is open (turned off) when the switch Q1 (106) is closed (turned on) to attach the solar module (102) (and the capacitor C1 (105)) to the serial power bus (103).

In some cases, a filter (not shown), including a serial coil and a parallel capacitor, is also used. The filter may be placed at the local management unit or placed just before the fuse box or inverter, or be part of either one of those.

In FIG. 2, the controller (109) is used to process the input signals (e.g., 104 a, 104 b, 104 c) and drive the switches Q1 (106) and Q2 (108). In one embodiment, the controller (109) is a small single chip micro controller (SCMC). For example, the controller (109) may be implemented using Application-Specific Integrated Circuit (ASIC) or Field-Programmable Gate Array (FPGA). The controller (109) can even be implemented in discrete, functionally equivalent circuitry, or in other cases a combination of SCMC and discrete circuitry. It will be generally referred to as single chip micro controller (SCMC) herein, but any implementation may be used.

In one embodiment, the controller (109) is coupled to the solar module (102) in parallel to obtain power for processing; and the controller (109) is coupled to the serial power bus (103) to obtain signals transmitted from other management units coupled to the serial power bus (103).

By switching the module (102) (or groups of cells, or a cell) on and off to the string periodically, the local management unit (101) may lower the voltage reflected to the string bus (103) (e.g., a lower average voltage contributed to the string bus) and can cause the current reflected to the string bus (103) to be higher, nearer the level it would be if the module was not weak, generating a higher total power output.

In one embodiment, it is preferable to use different phases to operate the switches in different local management units on a string to minimize voltage variance on the string.

In FIG. 3, the local management unit (101) provides two connectors (112 and 114) for serial connections with other local management unit (101) to form a serial power bus (103). The controller (109) controls the states of the switches Q1 (106) and Q2 (108).

In FIG. 3, when the controller (109) turns on the switch (106), the panel voltage and the capacitor C1 (105) are connected in parallel to the connectors (112 and 114). The output voltage between the connectors (112 and 114) is substantially the same as the output panel voltage.

In FIG. 3, during the period the switch (106) is turned off (open), the controller (109) turns on (closes) the switch (108) to provide a path around the diode D1 (107) to improve efficiency.

In FIG. 3, when the switch (106) is turned off (open), the panel voltage charges the capacitor C1 (105), such that when the switch (106) is turned on, both the solar panel and the capacitor (105) provides currents going through the connectors (112 and 114), allowing a current larger than the current of the solar panel to flow in the string (the serial power bus (103)). When the switch (106) is turned off (open), the diode D1 (107) also provides a path between the connectors (112 and 114) to sustain the current in the string, even if the switch (108) is off for some reasons.

In one embodiment, the controller (109) is connected (not shown in FIG. 3) to the panel voltage to obtain the power for controlling the switches Q1 (106) and Q2 (108). In one embodiment, the controller (109) is further connected (not shown in FIG. 3) to at least one of the connectors to transmit and/or receive information from the string. In one embodiment, the controller (109) includes sensors (not shown in FIG. 3) to measure operating parameters of the solar panel, such as panel voltage, panel current, temperature, light intensity, etc.

FIG. 3A shows an alternative three terminal implementation of the local management unit 101 shown in FIG. 3. In FIG. 3A, a panel voltage (180) is connected to terminals (182, 184). Terminals (182, 186) are connected to the string bus (103). A module driver (110) and a single chip micro controller (SCMC) control the switches Q1 and Q2. Under normal operating conditions, Q1 is on to allow normal operation of the system. When string current exceeds source capability, and as a result source voltage drops, Q1 and Q2 start a PWM (pulse width modulation) operation under control of the module driver (110). PWM involves modulation of duty cycle to control the amount of power sent to the load. This allows string current to remain constant, and input voltages can be maintained at the maximum power point. This implementation protects transistors during low voltage or short situations. In one embodiment, a single chip micro controller (SCMC) (109) can be connected in parallel to the diode D1 (107) to function in the manner of the SCMC 109 as described above. In one embodiment, the module driver (110) and the single chip micro controller (SCMC) (109) can be integrated in a single controller as shown in, for example, FIG. 3. As discussed above, single chip micro controller (SCMC) (109) can receive the inputs (104 a, 104 b, 104 c). As shown in FIG. 3A, in one embodiment, the inputs (104 a, 104 b, 104 c) are provided with a communications interface (not shown) coupled to a master controller (not shown). In one embodiment, other inputs (104 n) constituting information about other operating parameters can also be communicated to the single chip micro controller (SCMC) (109) from the communications interface. In one embodiment, the other inputs (104 n) can be information that is communicated bi-directionally. As discussed above, the power supply connections in the figures, including FIG. 3A, are not necessarily shown for purposes of clarity and so as not to obscure the invention.

FIG. 4 illustrates a photovoltaic system (200) according to one embodiment. In FIG. 4, the photovoltaic system 200 is built from a few components, including photovoltaic modules (201 a, 201 b, . . . , 201 n), local management unit units (202 a, 202 b, . . . , 202 n), an inverter (203), and a system management unit (204).

In one embodiment, the system management unit (204) is part of the inverter (203), the combiner box (206), a local management unit, or a stand-alone unit. The solar modules (201 a, 20 1 b, . . . , 20 1 n) are connected in parallel to the local management units (202 a, 202 b, . . . , 202 n) respectively, which are connected in series to form a string bus (205), which eventually is connected to an inverter (203) and the management unit (204). The solar module (201 a), for example, is connected to the local management unit (202 a) by the terminals (182, 184, 186) (FIG. 3A). As shown in FIG. 4, in one embodiment, the terminal (182), which connects to the panel voltage and the string voltage, is connected to the depicted left connection between the solar module (201 a) and the local management unit (202 a) and connected to the depicted left connection between the local management unit (202 a) and the string bus (205). The terminal (184), which is connected to the panel voltage, is connected to the depicted right connection between the between the solar module (201 a) and the local management unit (202 a). The terminal (186), which is connected to the string voltage, is connected to the depicted right connection between the local management unit (202 a) and the string bus (205).

In FIG. 4, the string bus (205) can be connected to the inverter (203) directly or as part of a mesh network or combiner boxes or fuse boxes (not shown). An isolated local management unit can be used as a combiner box (206) to adjust all voltages before connecting to the inverter (206); or, a single or multi-string inverter can be used. To limit the changes in the voltage of the bus, the management unit (204) may assign a different phase for each of the local management units (202 a, 202 b, . . . , 202 n). In one embodiment, at any given time, a maximum of a predetermined number of solar modules (e.g., one single solar module) are disconnected from the string bus (205).

In one embodiment, beyond the module connection the local management units can have the signal inputs, including but not limited to duty cycle (104 a), phase (104 b) and synchronization pulse (104 c) (e.g., to keep the local management units synchronized). In one embodiment, the phase (104 b) and the synchronization pulse (104 c) are used to further improve performance, but the local management unit (101) can work without them.

In one embodiment, the local management unit may provide output signals. For example, the local management unit (101) may measure current and voltage at the module side and optionally measure current and voltage in the string side. The local management unit (101) may provide other suitable signals, including but not limited to measurements of light, temperature (both ambient and module), etc.

In one embodiment, the output signals from the local management unit (101) are transmitted over the power line (e.g., via power line communication (PLC)), or transmitted wirelessly.

In one embodiment, the system management unit (204) receives sensor inputs from light sensor(s), temperature sensor(s), one or more each for ambient, solar module or both, to control the photovoltaic system (200). In one embodiment, the signals may also include synchronization signals. For example, a management unit can send synchronization signals periodically to set the timing values, etc.

Using the described methods the local management unit can be a very non-expensive and reliable device that can easily increase the throughput of a photovoltaic solar system by a few (e.g., signal or low double digits) percentage points. These varied controls also allow installers using this kind of system to control the VOC (open circuit voltage) by, for example by shutting off some or all modules. For example, by using the local management units of the system, a few modules can be disconnected from a string if a string is getting to the regulatory voltage limit, thus more modules can be installed in a string.

In some embodiments, local management units can also be used within the solar panel to control the connection of solar cells attached to strings of cells within the solar panel.

FIG. 5 illustrates a solar panel according to one embodiment. In one embodiment, the solar panel (300) has a few strings of solar cells (e.g., three solar cell strings per module). In FIG. 5, a local management unit (101) can be applied to a group of cells (301) within a string of an individual solar panel (300), or in some cases to each cell (301) in a solar panel (300).

In FIG. 5, a group of solar cells (301) that are attached to a local management unit (101) may be connected to each other in series, in parallel, or in a mesh configure. A number of local management units (101) connect the groups of the solar cells (301) in a string to provide output for the solar panel (300).

Some embodiments of the disclosure includes methods to determine the duty cycles and/or phases for local management units connected to a string or mesh of solar modules.

In some embodiments, the duty cycle of all local management units in a string or mesh can be changed, to increase or decrease the string voltage. The duty cycles may be adjusted to avoid exceeding the maximum voltage allowed. For example, the maximum voltage may be limited by the combiner box (206), the inverter (203), or any other load connected to the string bus (205), or limited by any regulations applicable to that system. In some embodiments, the duty cycles are adjusted to align the voltage of multiple strings.

In some embodiments, the duty cycle of one local management unit (101) in a string can be changed to cause higher current in that local management unit (101) and overall higher power harvesting.

In one embodiment, the duty cycles are computed for the solar modules that are connected to a string via the corresponding local management units. The duty cycles can be calculated based on the measured current and voltages of the solar modules and/or the temperatures.

After an initial set of duty cycles is applied to the solar modules, the duty cycles can be further fine tuned and/or re-adjusted to changes, such as shifting shading etc., one step a time, to improve power performance (e.g., to increase power output, to increase voltage, to increase current, etc.). In one embodiment, target voltages are computed for the solar modules, and the duty cycles are adjusted to drive the module voltage towards the target voltages.

The methods to compute the duty cycles of the solar modules can also be used to compute the duty cycles of the groups of solar cells within a solar module.

FIGS. 6-8 show methods to improve performance of a photovoltaic system according to some embodiments.

In FIG. 6, at least one operating parameter of a solar energy production unit coupled to a string via a management unit is received (401) and used to identify (403) a duty cycle for the management unit to connect the solar energy production unit to string. The solar energy production unit may be a solar module, a group of solar cells within a solar module, or a single solar cell in a string in a solar module. The duty cycle is adjusted (405) to optimize the performance of the solar energy production unit and/or the string.

For example, the duty cycle can be adjusted to increase the current in the string and/or the solar energy production unit, to increase the output power of the string and/or the solar energy production unit, to increase the voltage of the solar energy production unit, etc.

In FIG. 7, the operating voltages of a plurality of solar panels connected in series are received (421) and used to identify (423) a second solar panel having the highest operating voltage (highest output power) in the string.

In FIG. 7, a duty cycle of a first solar panel is computed (425) based on a ratio in operating voltage between the first and second solar panels. Alternatively, the duty cycle can be computed based on a ratio in output power between the first and second solar panels. Alternatively, the duty cycle can be computed based on a ratio between the first and second solar panels in estimated/computed maximum power point voltage. Alternatively, the duty cycle can be computed based on a ratio between the first and second solar panels in estimated/computed maximum power point power.

The duty cycle of the first solar panel is adjusted (427) to improve the performance of the first solar energy production unit and/or the string, until a decrease in the operating voltage of the second solar panel is detected. For example, the duty cycle of the first solar panel can be adjusted to increase the total output power of the string, to increase the current of the string, to increase the current of the first solar panel, to drive the voltage of the first solar panel towards a target voltage, such as its maximum power point voltage estimated based on its current operating parameters, such as temperature or a voltage calculated using its estimated maximum power point voltage.

In FIG. 7, in response to the detected decrease in the operating voltage of the second solar panel which had the highest operating voltage, the adjustment in the duty cycle of the first solar panel that causes the decrease is undone/reversed (429).

In FIG. 7, the duty cycle of the second solar panel is optionally decreased (431) to increase the operating voltage of the second solar panel. In some embodiments, the strongest solar panel (or strong panels within a threshold from the strongest panel) is not switched off line (e.g., to have a predetermined duty cycle of 100%).

In one embodiment, the duty cycle of the second solar panel is repeatedly decreased (429) until it is determined (431) that the decrease (429) in the duty cycle of the second solar panel cannot increase the voltage of the second solar panel.

In FIG. 8, operating parameters of a plurality of solar panels connected in a string are received (441) and used to identify (443) a first maximum power point voltage of a first solar panel. A second solar panel having the highest operating voltage (or output power) in the string is identified. A second maximum power point voltage of the second solar panel is identified (447) based on the received operating parameters and used to compute (449) a target voltage for the first solar energy production unit. In one embodiment, the target voltage is a function of the first and second maximum power point voltages and the highest operating voltage identified (445) in the second solar panel in the string. The duty cycle of the first solar energy production unit is adjusted to drive the operating voltage of the first solar panel towards the target voltage.

Alternatively, the target voltage may be the set as the first maximum power point voltage of the first solar panel.

In one embodiment, to adjust voltage a same factor is applied to all modules in that string. For example, in a case of a first module Al that is producing only 80%, and the voltage of the whole string needs to be 5% lower, the duty cycle of Al is 80% multiplied the duty cycle applied to the whole string (which is Y in this example) so module Al then has Y×0.8 as duty cycle.

In some embodiments, the system management unit (204) and/or the local management units (e.g., 202 a, 202 b, . . . , 202 n) are used solely or in combination to determine the parameters to control the operations of the switches.

For example, in one embodiment, a system management unit (204) is the “brain” of the system, which decides on the duty cycle and phase parameters.

For example, in another embodiment, each local management unit broadcasts information to the other local management units on the string to allow the individual local management units to decide their own duty cycle and phase parameters.

In some embodiment, a local management unit may instruct one or more other local management units to adjust duty cycle and phase parameters. For example, the local management units on a string bus (205) may elect one local management unit to compute the duty cycle and phase parameters for other local management units on the string.

For example, in some embodiment, the system management unit (204) may determine one or more global parameters (e.g., a global duty cycle, the maximum power on the string, the maximum voltage on the string, etc.), based on which individual local management units adjust their own duty cycles.

In some embodiments, a local management unit may effectively self manage and determine its own duty cycles without relying upon communicating with other management units. For example, the local management unit may adjust its duty cycle for connecting its solar module to the string to operate the solar module at the maximum power point. No local management unit is in control over the system, and each adjusts its own duty cycle (and thus, its power and voltage.)

In one embodiment, module voltage are measured by the local management units in the same string at substantially/approximately the same time and used to identify the strongest solar module. A strongest solar module provides the most power in the string. Since the modules are connected in series, the solar module having the highest module voltage in the string can be identified as the strongest solar module. In some embodiment, the operating voltage and current of the solar module are measured to determine the power of the solar module.

Additional approaches can be implemented to control the voltage, power output, or the efficiency of one or more strings of solar module controllers as described above. In some embodiments, a system controller management unit controls the operation of a plurality of local management units in one or more strings. In some embodiments, one or more local management units controls the operation of a plurality of local management units in one or more strings. In some embodiments, the local management unit may only control its own operation, or may control the operation of itself and other local management units in the same string.

One or more local management units in a string may have the capability to control the operation of other local management units in the same string. In one embodiment, a single local management unit can be selected to be a controlling local management unit to control a plurality panels in a string. The controlling local management unit in a string can be selected using any suitable protocol. In one embodiment, in a string of local management units, the first local management unit that announces its intent to take control of other modules in the string could become the controlling local management unit.

In one embodiment, to improve power output by a string, one or more local management units can each receive module voltage from all local management units in the same string and identify the strongest local management unit (i.e., the one with the maximum power and voltage). Each local management unit can then set its own duty cycle as a function of the received voltage.

In one embodiment, after the highest module voltage V_(m) in the string is identified, the duty cycle for each module can be computed as a function of a ratio between the module voltage V of the module and the highest module voltage V_(m). For example, the duty cycle for a module can be computed as 1−((V_(m)−V)/V_(m))=V/V_(m). In one embodiment, a particular local management unit receives the voltages of all other local management units at the same time or substantially same time (e.g., all voltages are received within an interval of less than one second.)

In one embodiment, the system management (204) may identify the highest module voltage from the module voltages received from the local management units (202 a, 202 b, . . . , 202 n), and compute the duty cycles for the corresponding local management units (202 a, 202 b, . . . , 202 n).

In one embodiment, the local management units (202 a, 202 b, . . . , 202 n) may report their module voltages on the string bus (205) to allow individual local management units (202 a, 202 b, . . . , 202 n) to identify the highest module voltage and compute the duty cycles, without relying upon the system management unit (204).

In one embodiment, one of the local management units (202 a, 202 b, . . . , 202 n) may identify the highest module voltage and/or compute the duty cycles for the other local management units (202 a, 202 b, . . . , 202 n).

In one embodiment, the duty cycles are determined and/or adjusted periodically (e.g., every 30 seconds). The intervals can take into account various environmental factors (e.g., where shadows on a solar panel are cast on different parts of the panel over the course of a day).

In one embodiment, after the duty cycles for the solar modules on the string are set based on the module voltage ratio relative to the highest module voltage in the string, the duty cycles can be fine tuned to increase the power performance. The duty cycles can be fine tuned one step a time, until a decrease of voltage of the module with the highest power is detected. In response to the detected decrease, the last change that caused the decrease can be reversed (undone). The fine tuning of the duty cycles can be used to reach the peak performance point (e.g., for maximum power point tracking).

In one embodiment, after the strongest module is identified, the duty cycles of the solar modules on the string are adjusted until the module with the highest power in the string decrease its voltage. Since decreasing the duty cycle of a solar module decreases the time period the module is connected to the string and thus increases its voltage, the duty cycle of the module with the highest power in the string can be decreased to increase its voltage, in response to the decrease in its voltage caused by the adjustment to the duty cycles of other solar modules on the string. For example, the duty cycle of the module with the highest power in the string can be decreased until its voltage is maximized.

The performance of solar modules may vary significantly with temperature. A system capable of measuring temperature can implement methods for controlling the voltage, power output, or the efficiency of one or more strings of solar module controllers using module temperature as a factor. In one embodiment, the local management unit measures module and ambient temperatures for some methods to determine the duty cycles. For example, the operating parameters measured at the local management units (e.g., 202 a, 202 b, . . . , 202 n), such as module temperature, can be used compute the estimated voltages of the solar modules at their maximum power points. For example, a formula presented by Nalin K. Gautam and N. D. Kaushika in “An efficient algorithm to simulate the electrical performance of solar photovoltaic arrays,” Energy, Volume 27, Issue 4, April 2002, pages 347-261, can be used to compute the voltage V_(mp) of a solar module at the maximum power point. Other formulae can also be used. Once the maximum power point voltage V_(mp) of a solar module is computed or estimated, the duty cycle of the solar module connected to a string can be adjusted to drive the module voltage to the computed/estimated maximum power point voltage V_(mp), since decreasing the duty cycle of a solar module normally increases its voltage.

In one embodiment, a local management unit may adjust the duty cycle of the solar module connected to the local management unit to change the module voltage to the computed/estimated maximum power point voltage V_(mp), without having to communicating with other management units.

In one embodiment, a local management unit (or a system management unit) may adjust the duty cycle of the solar module connected to the local management unit to perform maximum power point tracking.

In one embodiment, after identifying the strongest module and computing/estimating the maximum power point voltage V_(mpm) of the strongest module, the duty cycle for each module on a string can be computed as a function of a ratio between the maximum power point voltage V_(mp) of the module and the maximum power point voltage V_(mpm) of the strongest module. For example, the duty cycle for a module can be computed as 1−((V_(mpm)−V_(mp))/V_(mpm))=V_(mp)/V_(mpm). The duty cycle can be periodically updated, based on the current operating parameters measured, and/or fine tuned until a decrease in the voltage of the strongest module is detected.

Alternatively, a target voltage for each module on the string can be computed as a function of a ratio between the maximum power point voltage V_(mp) of the module and the maximum power point voltage V_(mpm) of the strongest module. For example, the target voltage for a module can be computed as V_(m)×V_(mp)/V_(mpm), where V_(m) is the measured voltage of the strongest module. The duty cycle of the module can be changed to drive the module voltage of the module towards the target voltage.

In one embodiment, after identifying the strongest module and computing/estimating the maximum power point power P_(mpm) of the strongest module, the duty cycle for each module on a string can be computed as a function of a ratio between the maximum power point power P_(mp) of the module and the maximum power point power P_(mpm) of the strongest module. For example, the duty cycle for a module can be computed as 1−((P_(mpm)−P_(mp))/P_(mpm))=P_(mp)/P_(mpm). The duty cycle can be periodically updated, based on the current operating parameters measured, and/or fine tuned until a decrease in the voltage of the strongest module is detected, since decreasing the duty cycle normally increases the module voltage.

In one embodiment, a target voltage for each module on the string can be computed as a function of a ratio between the maximum power point power P_(mp) of the module and the maximum power point power P_(mpm) of the strongest module. For example, the target voltage for a module can be computed as V_(m)×P_(mp)/P_(mpm), where V_(m) is the measured voltage of the strongest module. The duty cycle of the module can be changed to drive the module voltage of the module towards the target voltage, since decreasing the duty cycle normally increases the module voltage.

In one embodiment, the duty cycle for each local management unit is changed to increase the current of the solar module attached to the local management unit (e.g., based on the measurement of the voltage and current of the solar module), until the maximum current is achieved. This method assumes that string maximum power can be achieved with some accuracy by driving each local management unit to maximum current. In one embodiment, the voltages and currents of the solar modules are measured for tuning the duty cycles for maximum power point tracking for the string. The measurements of the voltages and currents of the solar modules also enable the local management units to additionally serve as a module level monitoring system.

The duty cycles can be adjusted by the system management unit (e.g., 204) based on the measurements reported by the local management units (e.g., 202 a, 202 b, . . . , 202 n), or adjusted directly by the corresponding local management units (e.g., 202 a, 202 b, . . . , 202 n).

In one embodiment, during the process of setting and/or tuning the duty cycles, the maximum power point tracking operation by the inverter (203) is frozen (temporarily stopped). Light intensity at the solar modules is monitored for changes. When the light intensity at the solar modules stabilizes, the voltage and current of the solar modules are measured for the determination of the duty cycles. Then normal operation resumes (e.g., unfreezing of maximum power point tracking operation).

In one embodiment, the local management units measure the voltages and currents of the solar modules to determine the power of the solar modules. After identifying the highest power P_(m) of the solar module on the string, the duty cycles of the solar modules on the string are determined by the power radio relative to the highest power P_(m). For example, if a module produces 20 percent less power, it will be disconnected from the string bus about 20 percent of the time. For example, if a module produces power P, its duty cycle can be set to 1−((P_(m)−P)/P_(m))=P/P_(m).

In one embodiment, a predetermined threshold is used to select the weak modules to apply duty cycles. For example, in one embodiment, when a module produces power less than a predetermine percent of highest power P_(m), a duty cycle is calculated and applied to the solar module. If the module is above the threshold, the module is not disconnected (and thus having a duty cycle of 100%). The threshold may be based on the power, or based on the module voltage.

In one embodiment, the system management unit (204) finds the duty cycles for the local management units (202 a, 202 b, . . . , 202 n) and transmits data and/or signals representing the duty cycles to the local management units (202 a, 202 b, . . . , 202 n) via wires or wireless connections. Alternatively, the local management units (202 a, 202 b, . . . , 202 n) may communicate with each other to obtain the parameters to calculate the duty cycles.

In one embodiment, the system management unit (204) knows all the different duty cycles indicated for the local management units (202 a, 202 b, . . . , 202 n).

In one embodiment, during power fine tuning, the system management unit (204) sends the appropriate data/signal to the appropriate local management units (202 a, 202 b, . . . , 202 n), and then the system management unit (204) calculates the total power of the string and corrects the duty cycle to produce maximum power. Once maximum power is achieved, the duty cycles for the local management units (202 a, 202 b, . . . , 202 n) may be saved in a database and serve as a starting point for the corresponding local management units (202 a, 202 b, . . . , 202 n) at the same time of day on the next day. Alternatively, a local management may store the duty cycle in its memory for the next day.

The stored duty cycles can be used when there is a fixed shade on the modules, such as a chimney, a tree, etc., which will be the same shade on any day at the same time. Alternatively, historical data may not be saved, but may be recalculated from scratch on each run, for example every 30 minutes.

In one embodiment, the light intensity at the solar modules is monitored for changes. The duty cycles are calculated when the light intensity does not change significantly. If there are changes in sun light radiation at the solar modules, the system will wait until the environment stabilizes before applying or adjusting the duty cycles.

In one embodiment, the system management unit (204) can communicate with the inverter as well. When the environment is not stable (e.g., when the sun light radiation is changing), the inverter may stop maximum power point tracking. In such a situation, the inverter can be set up for its load, instead of tracking for maximum power point. Instead of using the inverter to perform maximum power point tracking, the system management unit (204) and the local management units (202 a, 202 b, . . . , 202 n) are used to set the operating parameters and balance the string.

Alternatively, when the environment is not stable but measurements and calculation are done faster than the MPPT is working, there may be no need to stop the MPPT on the inverter. Alternatively, when the environment is not stable, measurements can be taken few times for the same radiation until a stable result is achieved.

Many variations may be applied to the systems and methods, without departing from the spirit of the invention. For example, additional components may be added, or components may be replaced. For example, rather than using a capacitor as primary energy store, an inductor may be used, or a combination of inductor and capacitor. Also, the balance between hardware and firmware in the micro controllers or processors can be changed, without departing from the spirit of the invention. In some cases, only some problematic modules may have a local management unit, for example in a shaded or partially shaded or otherwise different situation. In yet other cases, local management units of strong modules may be virtually shut off. The methods for determining the duty cycles for the solar modules can also be used to determine the duty cycles of groups of cells connected via local management units in a string within a solar panel/module.

FIG. 9 shows an overview of a local management unit (202 x) that is modified from the local management unit (101) discussed above in relation to FIG. 3A. In FIG. 9, local management unit (202 x) contains a single chip micro controller (SCMC) (109). In one embodiment, all of the features and details of the local management units discussed above apply to the local management unit (202 x) and are not repeated for purposes of clarity. In one embodiment, some of the features and details of the local management units discussed above selectively apply to the local management unit (202 x) and are not repeated for purposes of clarity. The module driver (110) is connected in parallel with the capacitor C1, and is also connected between the switches Q1 and Q2. The micro controller (109) contains various operating parameters regarding the local management unit (202 x), such as the voltage, current, etc. The micro controller (109) can run suitably programmed software (120 a-n) to modulate the chopping frequency of the switches Q1 and Q2. The switches Q1 and Q2 perform a duty cycle according to the formula calculated as previously described. A duty cycle would result in minor variations from cycle to cycle (i.e., in the inter cycle) that can be used to encode using MFM (modified frequency modulation), Manchester-type encoding, or other suitable time-delay type encoding technique with or without additional error correction. As discussed further below, the approach of modulating, for example, the PWM inter cycle would allow a receiver (301) at the end of the string bus (205) to measure the different variations of each of the local management units. Also, the local management units each can have a slightly different base frequency so that their respective harmonics would not cover each other, although they would move in a similar range. This approach has the added benefit of reducing overall EMI of the system.

FIG. 10A is a plot of the upper half of a frequency spectrum (500) of a carrier frequency (501) for a particular local management unit. The frequency spectrum (500) shows the harmonics fn1-fnn as elements (505 a-n). Arrows above the harmonics fn1-fnn (505 a-n) indicate they wobble around with the variations in pulse width modulation from cycle to cycle. Also shown is a notch filter curve (504), which can be used to remove significant noise to avoid EMI problems in the system and to comply with FCC and other regulatory agency regulations as needed.

FIG. 10B shows an overview of a subsystem (510) that includes the local management unit (202 x), the panel voltage (180), terminals (182, 184, 186), and a notch filter (506). In one embodiment, the notch filter (506) includes an inductor Ln and a capacitor Cn. The notch filter (506) acts as a low pass filter and relies on the internal capacity of the single chip micro controller (SCMC) of the local management unit (202 x). A notch frequency of the notch filter (506) sits on the switching frequency to suppress noise. In one embodiment, additional or different filters may be used.

FIG. 11A shows an overview of a system (200) with a string bus (205) similar to that of system (200) previously discussed in relation to FIG. 4. In FIG. 11A, a receiver subsystem (300) is a receiving portion of a modem associated with a head end to receive modulated signals from local management units, as described in more detail below. The receiver subsystem (300) includes a receiving path separate from the string bus (205) and the combiner box (206) so that the modulated signals from the local management units can be recovered before provision to the combiner box (206) and significant noise therein. The receiver subsystem (300) includes a receiver (301), a sensing line (302), and a data output line (303). The sensing line (302) is connected to the string bus (205) and the data output line (303) connects to the combiner box (206). In one embodiment, the subsystem (300) can be inside the inverter (203). In one embodiment, the subsystem (300) is contained in the combiner box (206). The subsystem (300) is shown external to the combiner box (206) in FIG. 11A for purposes of clarity.

FIG. 11B shows the receiver (301). The receiver (301) includes a band pass filter (310), a mixer (311), a beat oscillator (VCO) (312), a multiband pass filter (313), a microcontroller (314), and a power supply (315). Data from the local management unit arrives over the power bus 205 via sensing line (302), and then passes through the band pass filter (310) to improve signal-to-noise ratio. The mixer (311) mixes the output of the band pass filter (310) and the output of the VCO (312). The output of the mixer (311) is then applied to the multiband pass filter (313), where the signal is analyzed in multiple band, frequency, and time domains. The output of the multiband pass filter (313) is analyzed by the microcontroller (314). The power supply (315) can receive power from the string bus (205) or from the inverter (203) and provide it to the various elements of the receiver (301).

In one embodiment, the receiver (301) can manage communications from all the local management units. In one embodiment, each local management unit can have its own receiver. In one embodiment, a receiver can be implemented in hardware (HW) only. In one embodiment, a digital radio can be used as the receiver, in which case an analog to digital converter (ADC) samples the signals and all the processing is done in a microcontroller or a digital signal processor using software (SW), or any combination of SW and HW.

FIG. 12 shows a novel topology of a local management unit (1200) as a distributed converter and remaining aspects of the local management unit (1200), as discussed above, are not shown for purposes of clarity. In the energy production or photovoltaic system, the local management unit (1200) in FIG. 12 can be used alternatively to the local management units discussed above. The local management unit (1200) is a series-resonant converter with phase shift operation for light load operation. The local management unit (1200) includes capacitor Cin, switches Q1, Q2, Q3, Q4, inductor LR, capacitor CR, transformer having a primary winding Tp coupled to a secondary winding Ts, diodes D1, D2, and two capacitors Cout. A typical range of input voltage Vin for the local management unit (1200) is the standard panel voltage of V_(mp) plus or minus 20%. Output voltage Vout of the distributed converter is a fixed value of 375V plus or minus a few percentage points.

In operation, switch Q1 and switch Q2 are controlled oppositely, and switch Q3 and switch Q4 are controlled oppositely. When switch Q1 is on, switch Q3 is on. When switch Q2 is on, switch Q4 is on. The current can be increased or decreased by adjusting switches Q1, Q2, Q3, Q4. A controller (not shown), suitably connected to a power supply, controls the operation of the switches Q1, Q2, Q3, Q4. In one embodiment, the controller can be off the shelf and possibly modified. In one embodiment, the controller can have analog circuitry. In one embodiment, the controller can be a microcontroller. In one embodiment, the controller could be a combination of these features. As discussed below, a phase shift can be created between the currents controlled by the switches Q1, Q2, Q3, Q4. The inductor LR and the capacitor CR constitute an LC (or tank) circuit. The primary winding Tp of the transformer T is coupled to the secondary winding Ts. Diode D1, diode D2, and capacitor Cout constitute a Delon rectifier circuit. In a positive cycle, diode D1 charges the upper capacitor of capacitor Cout. In a negative cycle, diode D2 charges the lower capacitor of the capacitor Cout. Vout is effectively two times the voltage across the secondary winding Ts of the transformer T.

The local management unit (1200) requires a reliable current limit because it is required to charge a large input capacitance reflected from the inverter (203). The local management unit (1200) needs to allow operation with low input and output capacitance, because reliability does not allow the use of aluminum capacitors due to their limited life expectancy. In many instances aluminum may not be suitable for the local management unit (1200) for reasons of reliability.

Efficiency of the novel topology of the local management unit (1200) should be higher than 96 percent at the range of 20 percent to 100 percent load. The topology of the local management unit (1200) should allow direct control of input impedance for smooth MPPT control, and should minimize the need for damping networks (i.e., snubbers) in order to limit EMI emissions to improve reliability and maximize efficiency. Further, the transformer should be protected from saturation. Isolation voltage must be higher than 2000V, and switching losses reduced (i.e., zero current switching/zero voltage switching). No load condition is to be defined during inverter turn on.

The local management unit (1200) achieves the aforementioned performance goals. FIGS. 13 through 18 illustrate waveforms to show performance of the local management unit (1200) and the reduction of snub voltage transients without resort to a snubber network in the local management unit (1200). In FIG. 13, waveform 1302 shows the current through the primary winding Tp of the transformer T and waveform 1304 shows the drain voltage at the switch Q1 at the MPPT point. The waveform 1304 shows ringing on the square wave for only approximately two and a half waves at approximately one volt peak-to-peak.

In FIG. 14, waveform 1402 shows the current through the primary winding Tp of the transformer T and waveform 1404 shows the drain voltage at the switch Q1 at 30 percent load.

FIG. 15 shows low input voltage at full load condition. In FIG. 15, waveform 1502 shows the current through the primary winding Tp of the transformer T and waveform 1504 shows the drain voltage at the switch Q1 at full load condition. Steps (1503) in the waveform 1502 result from a phase shift between switches. The steps (1503) results is reduced undershoot and overshoot in the waveform 1504.

FIG. 16 shows output diode voltage at resonant frequency at maximum load. In FIG. 16, waveform 1602 shows the output current from the local management unit (1200) to the inverter (203) and waveform 1604 shows diode D1 (or diode D2) voltage at minimum frequency.

FIG. 17 shows typical output diode voltages at medium loads. In FIG. 17, waveform 1702 shows the output current from the local management unit (1200) to the inverter (203) and waveform 1704 shows diode D1 (or diode D2) voltage at minimum frequency.

For loads higher than 15 percent of the maximum load, switches Q1, Q3 are operated together at 50 percent duty cycle, while switches Q4, Q2 are operated together at 50 percent duty cycle with no phase shift. Input power is controlled by changing operating frequency of the local management unit (1200) above and below the resonant frequency. Turn ratio of the primary winding Tp and secondary winding Ts is set according to MPPT voltage because at this voltage efficiency is at the highest point (i.e., zero voltage, zero current is achieved). For other frequencies, switching is performed at zero voltage because there is current in the primary winding Tp and resonant tank that is maintained, and this current causes voltage shift that allows turn-on to be performed at zero voltage.

Below 15 percent of load, the local management unit (1200) is operated in phase shift mode. In phase shift mode, switches Q1, Q2 are reversed, and switches Q3, Q4 are reversed. However, a phase shift causes switches Q3 and Q4 to conduct together part of the time, and likewise for switches Q1, Q4. A phase shift operation allows no load and light load control. As shown in, for example, FIG. 15, steps 1503 in the waveform 1502 are caused by the phase shift. The phase shift range and frequency range are optimized for maximum efficiency by the local management unit (1200). The switches (primary transistors) do not have off spike because they are clamped to the input bus. The phase shift minimizes ringing (and overshoot and undershoot), which in turn increases efficiency, reduces EMI, and reduces heat losses. Secondary diodes D1, D2 are connected in center tap configuration to prevent voltage spikes from developing across them during turn-off and eliminating need for clamping components.

As shown in FIG. 16, a phase shift between the switches, as described above, causes a reduction in undershoot and overshoot in the diode D1 voltage without implementation of snubber networks. As a result, efficiency of the local management unit (1200) is improved both on the switch side and the diode side. In one embodiment, efficiency is improved on each side by approximately 1-2%.

In the local management unit (1200), a resonant tank provides a limit to the current through the primary winding Tp. A serial capacitor CR prevents transformer saturation. Output rectifier voltage is clamped to output voltage Vout allowing the use of 600V ultra fast diodes. There are no spikes across the switching transistors. Transformer parameters act as part of resonant tank. Input voltage range and efficiency are optimized for solar module operation by transformer turn ratio and transformer small air gap. Resonant frequency controls input impedance, which is the required control parameter for the application of separate solar modules operating against a fixed voltage inverter load in the system.

FIG. 18 shows a spectral waveform (1802) of typical emission characteristics of the local management unit (1200). Current ripple of the local management unit (1200) is measured with a current probe. Most of the current ripple comes from the inverter (203). In one embodiment, the inverter (203) is an off the shelf item. From the spectral waveform (1802), it can be seen that data transmission is possible but needs to be in the same level or higher level than the noise level. It can be seen that the maximum noise level value is approximately 35 dB. Switching frequency is clearly seen and can be detected in the spectral waveform (1802).

FIG. 19 shows a local management unit (1900) that can be used in accordance with the present invention. The local management unit (1900) can be used in place of the local management units discussed above. The local management unit (1900) includes a capacitor C1, switches Q1, Q2, diode D1, inductor L, capacitor C2, controller 1902, terminals 1904, 1906, 1908, and communication transmission modulator 1910. Operation of the local management unit (1900) is similar to the operation of the local management units, as discussed above. Data transmission by the local management unit (1900) involves modulating the switching frequency of the local management unit (1900) and transferring data by using the solar module itself as power amplifier (PA).

Operation of the local management units in FIGS. 1-3A and FIG. 12 involve pulse width modulation (PWM), as discussed above. The PWM technique creates noise, as shown in, for example, FIG. 18. The created noise can be modulated to transmit data over the string bus (205) from a solar module (or slave node) to a head unit (master) in the energy production or photovoltaic system. The use of noise in this way avoids the need to provide a costly separate, dedicated communications channel from the solar module to the head unit.

The communication transmission modulator (1910) modulates switching of the pulse width modulation (PWM) operation to transmit data from the local management unit (1900). Various modulation encoding schemes can be used, such as, for example, modified FM (MFM) and Manchester coding. In one embodiment, another modulating and encoding scheme can be used. In one embodiment, the communication transmission modulator (1910) represents the transmission portion of a modem (not shown) that is associated with the local management unit (1900). In one embodiment, the communication transmission modulator (1910) is part of the local management unit (1900). In one embodiment, the communication transmission modulator (1910) is external to the local management unit (1900).

This system allows the use of full duplex (two-way) communications. The receiver at the module side can be implemented within the module circuitry. The limitation of transmit and receive within same circuit does not exist. Transmission from management unit can be used to synchronize modules. Reliability is not affected by transmission. The effect on overall performance is very small because transmission duty cycle from module is low.

It is clear that many modifications and variations of this embodiment may be made by one skilled in the art without departing from the spirit of the novel art of this disclosure. These modifications and variations do not depart from the broader spirit and scope of the invention, and the examples cited here are to be regarded in an illustrative rather than a restrictive sense. In the foregoing specification, the disclosure has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. 

What is claimed is:
 1. An apparatus, comprising: a photovoltaic energy production unit to generate electricity; and a local management unit, coupled between the photovoltaic energy production unit and a connection of energy production units forming a string bus, the local management unit having a controller, a voltage converter having switching circuitry, and a communication transmission modulator; wherein the controller provides a control for the switching circuitry to cause the voltage converter to deliver electrical energy generated by the photovoltaic energy production unit to the string bus; and wherein the communication transmission modulator modulates the control, provided by the controller to the switching circuitry of the voltage converter, with data to be transmitted from the local management unit over the string bus.
 2. The apparatus of claim 1, wherein the controller employs pulse width modulation (PWM) to control delivery of the electrical energy by the switching circuitry.
 3. The apparatus of claim 2, wherein the communication transmission modulator modulates the control according to MFM (modified frequency modulation).
 4. The apparatus of claim 2, wherein the communication transmission modulator modulates the control according to Manchester encoding.
 5. The apparatus of claim 1, wherein the local management unit is a series resonant converter.
 6. The apparatus of claim 5, wherein the local management unit includes a transformer coupled to a rectifier circuit.
 7. The apparatus of claim 1, further comprising a notch filter connected to the local management unit.
 8. The apparatus of claim 1, further comprising a receiver, coupled to the string bus and a combiner box associated with an inverter, the receiver for receiving modulated signals from the local management unit.
 9. The apparatus of claim 8, wherein the receiver includes a receiving path separate from the string bus.
 10. The apparatus of claim 1, wherein the controller is configured to control the switching circuitry based on at least one of a duty cycle, a phase shift, and a synchronization pulse.
 11. The apparatus of claim 1, further comprising a single chip microcontroller, and wherein the controller is a module driver.
 12. A method, comprising: providing a local management unit to couple a solar energy production unit to a connection of energy production units forming a string bus, the local management unit having a controller, a voltage converter having switching circuitry, and a communication transmission modulator; providing, by the controller, a control for the switching circuitry to cause the voltage converter to deliver electrical energy generated by the photovoltaic energy production unit to the string bus; and modulating, by the communication transmission modulator, the control, provided by the controller to the switching circuitry of the voltage converter, with data to be transmitted from the local management unit over the string.
 13. The method of claim 12, wherein the providing a local management unit comprises: employing pulse width modulation (PWM) to control delivery of the electrical energy by the switching circuitry.
 14. The method of claim 12, wherein the providing a communication transmission modulator comprises: modulating the control according to MFM (modified frequency modulation).
 15. The method of claim 12, wherein the providing a communication transmission modulator comprises: modulating the control according to Manchester coding.
 16. The method of claim 12, wherein the local management unit is a series resonant converter.
 17. The method of claim 12, further comprising: receiving modulated signals from the local management unit.
 18. The method of claim 17, wherein the receiving modulated signals further comprises: receiving the modulated signals on a separate path from the string bus.
 19. The method of claim 12, wherein the providing a local management unit further comprises: controlling the switching circuitry based on at least one of a duty cycle, a phase shift, and a synchronization pulse.
 20. An energy generation system, comprising: a plurality of energy production units to generate electricity; a string bus providing a connection for the plurality of energy production units, wherein each of the plurality of energy production units includes: a photovoltaic energy production unit, and a local management unit, coupled between the photovoltaic energy production unit and the string bus, the local management unit including: a controller; a voltage converter having switching circuitry, wherein the controller provides a control for the switching circuitry to cause the voltage controller to deliver electrical energy generated by the photovoltaic energy production unit to the string bus; a communication transmission modulator configured to modulate the control, provided by the controller to the switching circuitry of the voltage converter, with data to be transmitted from the local management unit over the string bus; and a receiver connected between the string bus and a combiner box, the receiver configured to recover the data transmitted over the string bus. 